What actually makes a bike turn?

[ZooTech]

The idea that there is something called centrifugal force which has some bearing on the way a bike or other rotating body moves in relation to its environment is a mistaken one

Again, semantics. That's all your whole long-winded argument boils down to. The word "centrifigal" comes from the word "centrifuge", which is nothing more than a device which spins, usually to separate liquids of varying weight (like plasma from blood). While the use of the word "centrifigal force" is technically incorrect in the context of spinning motorcycle wheels, the underlying point is clearly conveyed. While the pippity-poppity members of acedemia, in their corduroy jackets with leather elbows, may scoff at its misuse, we here at TMW are forgiving enough to allow it to be used interchangeably with the word "gyroscopic" when referencing the forces created by a spinning wheel. And your attempt to build an entire argument around this minor semantic faux pas is juvenile.

[sv-wolf]

I have no personal motivation...think about it. I have nothing to gain by your personal salvation. And, I'm not at all interested in winning an arguement. That's why I asked you to PM me for details if you want them. If you'd rather publicly stand against my absolute belief in the truth I believe, that's up to you...I was simply offering to you what I believe to be true, and I also believe you would benefit from it...not me. I won't respond publicly again, but I will publicly apologize for misinterpreting your statements...I obviously did, and I'm sorry.

Thanks Ron. I appreciate your reply. That was generous of you.

The truth is I love a good debate and to be honest, the subject matter doesn't matter much.

By the way, I'm perfectly aware of 'forces that are clearly felt' both physical and spiritual, but we clearly differ in their interpretation My attitude to spiritual experience is complex (though not Christian) but as it is also personal I don't tend to use it as a subject of discussion.

Best wishes and ride safely, Ron

Regards

Richard

[niterider]

Okay, lets see if I learned anything. The certifigal force generated by the wheels oposse the change of direction all the while that the bike is into a turn. And the graitational force tries to pull bike and rider to the ground, the centrifugal force generated by the turning bike counter balances the gravitational force. That is amasing, all this happening at once, and we are still able to enjoy the ride.

[sv-wolf]

The idea that there is something called centrifugal force which has some bearing on the way a bike or other rotating body moves in relation to its environment is a mistaken one

While the pippity-poppity members of acedemia, in their corduroy jackets with leather elbows, may scoff at its misuse, we here at TMW are forgiving enough to allow it to be used interchangeably with the word "gyroscopic" when referencing the forces created by a spinning wheel. And your attempt to build an entire argument around this minor semantic faux pas is juvenile.

Oh God Zoo, what's eating you!!!!!

Thank you for letting me know this at last. I have never heard the term centrifiugal used to mean 'gyroscopic' before. You could have just told me without going into sarcastic hate mode.

But that is not the way I was using the phrase, nor was it the way Sev was using it. The role of gyroscopic forces in cornering is not what our debate was about.

And this is more than a matter of semantics. Please re-read my posts. The 'pippity poppity members of academica' (nice turn of phrase, by the way) can choose to use the term any way they like, but the issue turns on the understanding of what forces are acting on a bike when it is cornering.

Frankly, it doesn't bother me one way or another how people choose to understand what happens. That is up to them. If it works for them, fine. What I orignally commented on was that people who should know better, draw diagrams in textbooks which include non-existent forces. That annoys me, since anyone who does want to approach this mathematically is going to be misled. I sounded off on the forum. Sev chose to challenge me on it and the debate followed.

I can't resist a good argument.

I'm glad you feel you can speak for the site, Zoo

[sv-wolf]

As long as we're all up and getting annoyed I'm irritated that you never actually bothered to read what I had to say, and simply replied to catch phrases.

That being said I don't think this thread is going anywhere anymore. So lets all just agree that somewhere along the lines the rider makes the bike do something that makes it turn. And let the thread die before something we all regret is said.

Actually Sev, to be truthful, I couldn't make head or tail or what you were talking about a lot of the time. Despite what you think, I did do you the courtesy of having a long think about what you said in each post before replying. I have to say, you made it very difficult for me by dodging between a real force and an unreal one and I wasn't clear whether you realised you were doing it. In retrospect, what I should have done was ask you to clarify. That would have been a more friendly approach. So, a useful lesson learned.

And I've no intention of falling out with you over this.

Thanks for a good ding dong.

Best wishes

[shane-o]

If ya wanna feel the "gyroscopic" forces applied to a spinning wheel in its truest form...pick up a 9" anglegrinder, hit start = approx 10000 rpm, then try tilting the spinning disk. It kinda feels like a bike when ya wiggle the bars at high speed.


Im thinking, if ya apllied some remotes to all the bike controlls, and could remote pilot the bike, when you input a push on the right bar of the riderless bike at 60mph, the bike will lean and turn right.

thus ya cant turn without leaning, and ya use the bars to initiate the spinning wheel to tilt from which ya then are forced into positioning yourself into a lean angle appropriate to the turn.

and Im spent

[niterider]

Buy a remote control toy bike and see the way it works. It runs on two wheels just like the real bike. The spin of the wheels keep it up-right.

[storysunfolding]

Ok guys.

I'm sorry

You have it all wrong.

I read through all your explanations and I'm sure you "know" physics but you still don't know what you're talking about.

It isn't turning the handle bars, it isn't lean, it's how you move your butt.

That's right, your rear has all the power. When my rear wiggles right, my bike goes right, when it wiggles left, my bike goes left. When I listen to latino music and my butt gets the wiggle I can't control the bike. When I listen to some crazy pop music, I crash. All your power is in the rear.

MAYBE there are a few other things that make a bike turn, but in the end, it's your butt.

And some of you with a few extra pounds can obviously out maneuver me with your massive bike control.

*intended for joke purposes only* Thanks for the long writeups from everyone- it's been interesting

[Posthumane]

Geez, I leave for a few days, and this is what happens....
Anyway, I hope I'm not stepping on anybody's toes by reviving this thread, but I would like to continue the discussion with sv-wolf about the physics involved in cycle steering.

You make an interesting point about the tire profile, and while it is obvious that the inside edge of the contact patch will travel a shorter distance than the outside during a turn, I don't think this is a very significant factor in causing the bike to turn (I think, if anything, this helps generate heat in the tire due to scrub). The reason I think this is as follows. If the turning force was generated by the profile of the tire, the bike would have to turn about the point in the centre of the contact patch. This works fine in a unicycle, but would not work on a bicycle (or motorbike) due to the fact that the bike has a significant (non-zero) wheelbase. The turning action of the rear tire profile would cause lateral front tire scrub and vise versa. However, this scrubbing action can easily be taken up by tire slip, making my point sligtly moot, which brings me to my second reason for not believing this to be a significant force.

Most motorcycles have rather wide tires, but many bicycles do not. This does not cause them to develop any less cornering force or have a larger turn radius. A racing bicycle has a tire that is not much more than 1cm wide. Even if the inside edge of the contact patch were travelling significantly slower than the outside edge (which it really doesn't due to the large diameter of the tire and small difference in diameter between the edge and centre of the tire), the lack of lateral distance between the two would prevent a significant turning moment from being generated. I would venture to say that a bike with inifinitely thin tires would be just as easy to turn as a bike with a wide, round section tire, as can be demonstrated by rolling a very thin disc or coin along the ground.

My example of skis and square section tires was not very good because both have the ability to flex (as does a round section tire) distorting their shape. As an aside, the original Boss Hoss (chevy v8 powered bike) had a car tire (square section) on the rear, and was still able to be ridden, though I've read that the handling was not up to par.

What I meant in my earlier post about the front steering in relation to the rear was that, in spite of the driver's input causing the front wheel to steer away from the natural direction of travel, it is still turned away from the cycle's centerline towards the direction of lean. Let me try to explain this with an example as it sounds confusing without a diagram. The rider is coming up to a left hand turn. He initiates the turn by turning the wheel to the right of the cycles centreline, causing the bike to lean to the left. If the rider were to rigidly hold the wheel in that exact orientation, the bike would continue that leaning motion at that current rate until it hit the ground. If the rider were to let go of the handlebars (slowly) the wheel would turn towards its natural path of travel (well left of the bike's centreline) and the bike would right itself. The rider does neither of these things, but rather leaves some pressure on the bars to keep the wheel turned to the right of its natural path of travel, but to the left of the bikes centreline, allowing the cycle to travel around the corner without straightening or falling over.

Phew, that was a long post. Anyway, I don't know of any published technical papers on this subject (though there probably are some). All of the above was derived through my own personal observation, and logical deduction. I await your reply.

[sv-wolf]

Hi Posthumane, that's a really intriguing set of observations. I've always found this issue of what turns a bike quite puzzling, Until now, the argument about the differential speed on the two sides of the patch has been almost the only one that has made any sense to me. Now, I'm not sure. There is one other, but I won't muddy the waters here with it, at least yet.

Your own explanation of what does the job is not one I've heard before. In its own terms, it sounds very plausible, though I'd like to think about it some more and do a few observations of my own. In the meantime, I'll give you my first thoughts on these matters.

Your first observation, with regard to scrub, had me going for a moment, but I don't think it supports your general argument. To keep things simple, I'll start with your unicycle. Unless I misunderstand you, I don't think a tyre would have to turn about the point in the centre of the contact patch - unless the unicycle were literally turning on the spot. It would turn about the centre of the unicycle's turning circle. Disgarding for the moment any distortion in the tyre at the point of contact, there would be no more scrub from a single turning tyre than there would be slippage from say a pair of bevel gears, or from a cone or conical section rolling round on a flat, horizontal surface.

On a bike, which, as you say, has a significant wheelbase, there would be more of an issue with 'scrub'. But I can't see it being a significant one. In any realistic curve a bike might have to make the length of arc between the tyres would not be great in comparison to the radius of the turn, so that any scrub could be mopped up by tyre slip - as you yourself observe.

Your second, empirical point about the bicycle tyre is more imediately convincing, and at this point, you've mostly sold it to me.

The turning force arising from the contact patch is, as you say, clearly related to the tyre's radius of curve. Therefore, on the face of it, if the different rates of turn across contact patch were responsible for turning the vehicle, you would expect a bicycle to have much less ability to turn than a motorbike. However, it also occurs to me that the turning force on the patch is not just related to tyre radius, but to the radial angle of the contact patch. The contact patch on a bicycle tyre is much larger in relation to tyre section than it is on a motorbike, and the differential forces would therefore be greater. Even so, it doesn't sound likely that this would make enough difference to account for the similar handling, but sometimes when you do the maths, the results can be surprising.

I really don't know. What do you think?

Looking at your own explanation of why a bike turns for a moment, the main doubt I would have would be similar to the one you have introduced about the sufficientcy of the contact patch on a bicycle. If, as you say, on a left hand turn, the front wheel steers to the left of the centreline (even though there is a small countersteering element to the right) would this ever be sufficent to explain a sportsbike's ability to turn sharply? It's a matter of degree again. It may be that it does. Again, I don't know. I'll have to get out on my bike, and check this one out as far as I can empirically.

I suspect the answer to all this lies somewhere in the behaviour of your thin disc. Will think some more.

In the meantime, thanks for your thoughts. I feel a lot more uncertain about this issue than i have for a while - but that is no bad thing. However, if the contact patch is not the answer, then I hope your explanation is!!!

Cheers

Boy, am I glad this wasn't another issue about centrifugal force.